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Reddit-runner t1_j29wl7p wrote

Reply to comment by stewartm0205 in What if we kept pursuing nuclear spacecraft propulsion? by rosTopicEchoChamber

NTR also died because of their cost, difficulty to repair them during the mission (or even after) and the volume of the propellant.

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stewartm0205 t1_j2au6yp wrote

Repair? No one repairs rocket engine especially back then. And volume of propellant shouldn’t be a big deal since ISP would be two to three times H2 + O2 if you needed a high enough delta V.

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Reddit-runner t1_j2ax7a8 wrote

>No one repairs rocket engine especially back then

Right. Not even after a static fire test.

But one idea was to use NTR tech in a reusable space tug. Reusability is very difficult to achieve if you can't even maintain your engine.

With that limitation NTR was confined to single use missions. Like pushing something to Mars and then getting deposited in a solar orbit.

But for such a use case NTR doesn't offer much advantage over LH2/LOX. The tanks need to be enormous, they need heavy insulation against boil-off, the NTR engines need heavy shielding, thrust is low, etc.

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stewartm0205 t1_j2bs81v wrote

In space, a NTR wouldn’t need much shielding. In space, a tank wouldn’t need much insulation.

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Reddit-runner t1_j2ctl6v wrote

Wrong.

You need heavy shielding to not irradiate the payload

And the insulation is necessary because the tanks are in constant exposure to the sun.

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stewartm0205 t1_j2fin05 wrote

The reactor is at the other end of the rocket far away from the payload in the high radiation environment of space. At worse, a small block of material should be enough of a shield. The radiation will dissipate at square the distance from the reactor. Then it had to penetrate the liquid hydrogen in the tank. As for the tank, a shiny thin Mylar sheet would be enough to reflect the rays of the sun. The Vacuum of space makes for a perfect insulator.

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Reddit-runner t1_j2fxmzm wrote

> The Vacuum of space makes for a perfect insulator.

Yeah, that's the problem. Do the math

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